The present invention relates to motor vehicle security systems.
In a common type of prior art motor vehicle anti-theft security system, the system is sequenced into an "armed" mode after the engine is stopped, the vehicle parked, and the user exits the vehicle and closes all of the doors. This system detects tampering/illegal entry by sensing a voltage on the door/courtesy light circuit or by a vibration/position sensor, which triggers an annoying alarm and causes interruption of the engine starter circuit. Such alarm is typically announced via flashing lights, honking horn or siren. However, these systems are prone to false alarms, which create unnecessary noise pollution, and can even be the subject of expensive traffic fines in some municipalities.
The typical system of the above type must be disarmed prior to vehicle reentry in order to avoid triggering the alarm, and the starter circuit will not function until the system is disarmed. Typically the vehicle user is able to arm or disarm the security system by means of a coded, hand-held, RF transmitter. These RF devices require a high degree of security coding in order to prevent their codes from being broken by code-scanning devices. Alternatively, some systems automatically arm/disarm according to use of the ignition key to start or stop the engine.
The typical prior art system includes an electronic control module which is installed under the dash board adjacent to the steering column and is connected to the keyed ignition switch. This arrangement is typically rather easy to jumper (hot-wire). This control module typically has a starter circuit interrupt device which is spliced in series with the starter circuit between the starter relay and the ignition switch. As well, because such starter interrupt is fairly easy to defeat by hot-wiring at the ignition switch or over the cutout device, the better prior art systems include a self-holding cutout relay located in the engine compartment. In the latter case, when the armed system is triggered, the thief cannot defeat the system from inside of the vehicle; rather, the thief must open the hood of the vehicle engine compartment and defeat the interrupt. While the thief may still be able to directly hot-wire the starter and thus to defeat a starter circuit interrupt in the engine compartment, it is believed that the average thief will not have the time for such extra attention attracting activity in defeating the interrupt. A hood lock may be installed to further foil the thief.
Still furthermore, vehicle hijacking is now a present concern in some cities. In the typical situation, the authorized user-motorist is pulled from the vehicle after the user has disarmed the security system and has started the engine. Now the thief can drive the vehicle away without concern about triggering an armed security system and without the need for hot-wiring.
It is therefore an object of the present invention to provide a vehicle security system which is difficult to defeat.
It is another object of the present invention to provide a security system which can protect against vehicle hijacking.